Surface passivation of phosphorus-diffused n(+)-type emitters by plasma-assisted atomic-layer deposited Al2O3

In recent years Al2O3 has received tremendous interest in the photovoltaic community for the application as surface passivation layer for crystalline silicon. Especially p-type c-Si surfaces are very effectively passivated by Al2O3, including p-type emitters, due to the high fixed negative charge in the Al2O3 film. In this Letter we show that Al2O3 prepared by plasma-assisted atomic layer deposition (ALD) can actually provide a good level of surface passivation for highly doped n-type emitters in the range of 10-100 Omega/sq with implied-V-oc values up to 680 mV. For n-type emitters in the range of 100-200 Omega/sq the implied-V-oc drops to a value of 600 mV for a 200 Omega/sq emitter, indicating a decreased level of surface passivation. For even lighter doped n-type surfaces the passivation quality increases again to implied-V-oc values well above 700 mV. Hence, the results presented here indicate that within a certain doping range, highly doped n- and p-type surfaces can be passivated simultaneously by Al2O3. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim